Native and modified starches have been used for many years in the food industry to provide processed foods with improved product appearance and increased consumer appeal. Starches can impart desirable properties to food products, ranging from shape retention and sliceability to desirably grainy and pulpy textures in sauces and dressings. Sources of starch include roots, root-like or tuber plants and cereals.
When native starch granules are dispersed in excess water and heated they become hydrated and swell. The swelling of the granules results in an increase in viscosity which, in unmodified starch, peaks at temperatures in the range of 56° to 95° C. This increase in viscosity is a desired property in many food and industrial applications. Swollen, hydrated starch granules, however, are quite fragile. When a granular starch slurry is maintained at temperatures greater than 80° C., the starch granules begin to fragment and the viscosity breaks down. Shear or conditions of extreme pH also tend to disrupt and fragment the granules, so that the starch polymers dissociate and become solubilized, leading to a rapid breakdown of the initially high viscosity.
Both the swelling of the starch granules and the breakdown in viscosity can be inhibited by treating the starch with chemical reagents that introduce covalent intermolecular bridges or crosslinks between the starch molecules. The crosslinks reinforce the associative hydrogen bonds holding the granules together, restricting the swelling of the starch granules, which inhibits the disruption and fragmentation of the granules. This allows the starch to delay solubilization during cooking and results in a desirably “shorter” texture instead of a “slimy” and cohesive texture.
A reduction in the disruption and fragmentation of the granules can also be achieved according to the method described in U.S. Pat. No. 5,718,770 wherein the thermal treatment of starch granules results in properties characteristic of the crosslinked starches. Accordingly, chemically crosslinked or thermally inhibited starches are used in many applications where a stable viscosity starch paste is needed.
Other means of reducing the rapid breakdown in starch solution viscosity have been explored. For example, U.S. Pat. Nos. 5,424,088 and 4,298,729 describe a composition of a carboxylated polymer, which may be xanthan, and starch which is characterized by reduced dissolution in water and increased acid, heat and shear stability. Both processes require that the starch be at least partially gelatinized (solubilized). Because of the resultant increase in viscosity caused by the partial gelatinization, the process is limited to relatively low solids contents and drying becomes an undesirably energy-intensive process. Further, since gelatinization disrupts the starch granule, solutions of the xanthan/starch compositions are unable to maintain a satisfactorily high viscosity or provide delayed gelatinization during cookout.
Carboxylated polymer and starch compositions have been investigated for use in a variety of applications. For example, WO 00/32064 describes a controlled-release, digestible carbohydrate material (possibly starch) which is coated, encapsulated, entrapped or embedded in a crosslinked polysaccharide matrix. U.S. Pat. No. 5,895,804 describes a thermosetting system which may comprise a polysaccharide (including starch) and a carboxylated polymer. However, both of these systems require high amounts, greater than 5% by weight, of the expensive carboxylated polymer.
There is an ongoing need to provide starch compositions which are able to address the problem of breakdown in starch viscosity and do not require high levels of expensive components, toxic chemicals and an energy-intensive processes.
The present invention provides a process for obtaining a novel, granular starch modified by less than 5% by weight of carboxylated polymer which possesses these properties to a degree exhibited only by chemically crosslinked or thermally inhibited starches. The invention further relates to the improved foods prepared from these composites.